Research On Straw Decomposition And Soil Organic Carbon Balance As Affected By Long-term Straw Incorporation In The Continuous Cropping Cotton Field

Xinjiang is an important commodity cotton base in our country, and the yield accounts for about 2/5 of the total cotton yield in our country. Due to its large planting area and continuous cropping in a long time,there are so many serious phenomenon in soil such as the soil-borne diseases induced, the soil enzyme activity declined, and so on, being the bottleneck in the development of cotton production. Straw return is an important measure to sustain the development of agriculture and relief the obstacle of continuous cropping. However, the straw will release some allelochemicals after it is leached by snow or rain,exacerbating the obstacle of continuous cropping. Investigating the straw decomposition and soil organic carbon balance can provide a basis for evaluating soil quality and fertility, therefore, our experiment is carried out in the cotton field that includes different years of continuous cropping, investigating the changes of straw decomposition and soil organic balance in the different year of continuous cropping cotton field.The results were shown as follow:1. The above ground and the root of cotton straw decomposition behaved “quicker-slower-quicker”. The above ground of straw in the 1 a, 10 a and 20 a treatments declined rapidly during 0~43 d and 193 d~365d, but slower during 43~193 d. The variation of cotton root dry biomass in 10 a and 20 a treatment was similar to the above ground, the exception was that the cotton root dry biomass declined rapidly during43~177 d and 193~365 d. After 365 d, the above ground and root of cotton straw decomposition rate was47% ~ 58% and 39% ~ 59%, respectively. Compared with 1a treatment, continuous cropping could accelerate the cotton straw decomposed during the first 16 d, but there was no significant difference in decomposition rate among different continuous cropping treatments.2. After the cotton straw decomposed for a year, too much cellulose and hemicellulose and soluble sugar were released, and the rest of them released slowly. Continuous cropping have no effect on the release of cellulose, hemicellulose and soluble sugar, but it have significant effect on lignin decomposed.3. After 193 d, 95~97% of straw K had been released compared with 29~34% of straw P, 40~50% of straw N, and 35%~40% C. The model of nutrient release was directly release, and the nutrient release rates decreased in the order K > N > C > P. After that, we could know that 60% C in soil was fixed after the straw return, meanwhile, the straw also provide N and K for soil, but it could release a little P. Therefore,When we fertilized in the field, we could reduce the input of N and K, and increase the P content.4. In 1a treatment, when the rate of straw incorporation reached 72.04%, the soil organic carbon in 0~20cm could be balanced, the value was 11.84 g·kg-1. With the duration increased, the soil organic carbon content and storage were both increased gradually, when the duration reached the 28 year, 30 year and 39 year, respectively, the soil organic carbon in the 0~20 cm, 20~40 cm and 40~60 cm layer could be balanced again, respectively. The value was 17.2 g·kg-1, 15.38 g·kg-1 and 12.72 g·kg-1.5. There was significant positive correlation between the soil organic carbon storage in 0~60 cm soil layer and straw carbon input. As for the speed of soil organic carbon, the soil organic carbon storage increased rapidly in 5 years, after that, it increased slowly, when the duration reached the 26 years, the soil organic carbon storage got the maximum value( 112.2 t·hm-2).